High-spin yrast levels of 38Ar

High-spin states of ³⁸Ar have been studied with the ³⁵Cl(α, pγ)³⁸Ar reaction at E_α = 18 MeV and with the ²⁴Mg(¹⁶O, 2pγ)³⁸Ar reaction at $\text{E(}{}^{16}\text{O}\text{) = 38}\text{and}\text{45}\text{MeV}$. The ³⁸Ar level scheme is obtained with the former reaction from a proton-γ coincidence measurement. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization experiments have been performed with a Ge(Li)-Na(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{= 7}{}^{\mathrm{?}}\text{, 7}{}^{\mathrm{+}}\text{, 8}{}^{\mathrm{+}}\text{, 7}{}^{\mathrm{?}}\text{, 9}{}^{\mathrm{?}}\text{and}\text{11}{}^{\mathrm{?}}$to the ³⁸Ar levels at E_x = 7.51, 8.08, 8.57, 8.97, 10.17 and 11.61 MeV, respectively, are obtained. The 8.57 MeV, 8⁺ level has a mean life below 0.8 ps. Excitation energies, branching ratios, multipole mixing ratios and transition strengths are reported. The experimental results are compared with shell-model calculations.     

Competition cusps in (α, γ) reactions

Absolute cross sections are presented for the reactions ³⁷Cl(α, γ)⁴¹K for 2.90 MeV ≦ E^lab_α ≦ 5.23 MeV, ${}^{62}\text{Ni}\text{(α, γ)}{}^{66}\text{Zn}\text{for}\text{5.07}\text{MeV}\text{≦ E}{}_{\mathrm{\alpha }}{}^{\mathrm{?2}}\text{lab}\text{≦ 8.64}\text{MeV}\text{,}{}^{62}\text{Ni}\text{(α,}\text{n}\text{)}{}^{65}\text{Zn}$ for energies near the (α, n₀) threshold at $\text{E}{}_{\mathrm{\alpha }}{}^{\mathrm{<mtext>lab</mtext>}}\text{= 6.90}\text{MeV up to}\text{8.76}\text{MeV}\text{,}{}^{64}\text{Ni}\text{(α, γ)}{}^{68}\text{Zn for}\text{4.50 ≦ E}{}_{\mathrm{\alpha }}{}^{\mathrm{<mtext>lab</mtext>}}\text{≦ 7.45}\text{MeV}$, and for ⁶⁴Ni(α, n)⁶⁷N from E_α^lab = 5.30 MeV up to E_α = 7.45 MeV. Substantial competition cusps were observed in the excitation function for all three (α, γ) reactions. The data were found to be in reasonable agreement with the predictions of the current versions of global Hauser-Feshbach models used in nucleosynthesis calculations. Including width fluctuation corrections and realistic neutron strength functions generally improves the ability of the models to predict the depth of the (α, γ) competition cusps; the depths of the predicted (α,γ) cusps are insensitive to the degree of isospin mixing. Taken together with studies of competition effects in proton-induced reactions, the present data confirm the importance of width fluctuation and strength function effects, and indicate essentially complete isospin mixing between T^< and T^> states in the compound nucleus.     

Spectroscopy of states in 33S by means of neutron-gamma angular correlation measurements

Levels of ³³S for E_x < 5 MeV have been studied with the ³⁰Si(α, nγ)³³S reaction at bombarding energies of E_α = 7.5 and 10.2 MeV. Neutron-gamma angular correlation experiments lead to three unambiguous spin and parity assignments: $\text{J}{}^{\mathrm{\pi }}\text{(3.83) =}\text{5}\text{2}{}^{\mathrm{+}}\text{, J}{}^{\mathrm{\pi }}\text{(4.048) =}\text{9}\text{2}{}^{\mathrm{+}}\text{and}\text{J}{}^{\mathrm{\pi }}\text{(4.09) =}\text{7}\text{2}{}^{\mathrm{+}}$. The measured branching and mixing ratios yield transition strengths for dipole and quadrupole transitions.     

Das Niveauschema von 47V aus dem γ-zerfall von Analogresonanzen

A high-accuracy investigation of the level scheme of ⁴⁷V has been performed using the ⁴⁶Ti(p, γ)⁴⁷V reaction. The γ-decay schemes of the strong (p, γ) resonances at E_p = 1546, 1549, 1565 and 1572 keV lead to 17 new energy levels in ⁴⁷V with excitation energies between 2.7 and 5.1 MeV. From the (p,γ) angular distributions mixing ratios of the primary γ-transitions and J^π values of the resonances and of many states populated in the γ-decay have been determined. The total width of the E_p = 1549, 1565 and 1572 keV resonances for γ-decay are found to be Γ_γ = 0.12, 0.15 and 0.03 eV, respectively. The Q-value of the ⁴⁶Ti(p,γ)⁴⁷V reaction is found to be 5168.6 keV. The two resonances at E_p = 1549 and 1565 keV, which have $\text{J}{}^{\mathrm{\pi }}\text{=}\text{3}\text{2}{}^{\mathrm{?}}$, are interpreted as fine structure components of the analogue state of the $\text{E}{}^1\text{= 2.545}\text{MeV}\text{J}{}^{\mathrm{\pi }}\text{=}\text{3}\text{2}{}^{\mathrm{?}}$ level in ⁴⁷Ti while the ($\text{7}\text{2}$) resonance at E_p = 1546 keV might correspond to the $\text{E}{}^1\text{= 2.615}\text{MeV}\text{7}\text{2}{}^{\mathrm{?}}$ parent state in ⁴⁷Ti. The analogue-antianalogue M1 transition strength of the split $\text{3}\text{2}{}^{\mathrm{?}}$ analogue state is 0.01 single-particle units and fits well into our systematics of IAS → AIAS transitions in fp-shell nuclei.     

High-spin states of 39K and 42Ca

High-spin states of ³⁹K and ⁴²Ca have been investigated with the ²⁸Si(¹⁶O, αpγ)³⁹K and ²⁸Si(¹⁶O, 2pγ)⁴²Ca reactions at a beam energy of 45 MeV. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization measurements were performed with a Ge(Li)-NaI(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. High-spin states of ³⁹K at E_x = 7.14,7.78and8.03 and of ⁴²Ca at E_x = 7.75MeV are established. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{=}\text{11}\text{2}{}^{\mathrm{?}}\text{,}\text{13}\text{2}{}^{\mathrm{?}}\text{,}\text{15}\text{2}{}^{\mathrm{+}}\text{,}\text{15}\text{2}{}^{\mathrm{?}}\text{,}\text{17}\text{2}{}^{\mathrm{+}}\text{and}\text{19}\text{2}{}^{\mathrm{?}}$ to the ³⁹K levels at E_x = 5.35, 5.72, 6.48, 7.14, 7.78 and 8.03 MeV and of 6^?, 7^?, 8^?, 9^? and(8, 10)^? to the ⁴²Ca levels at E_x = 5.49, 6.15, 6.41, 6.55 and 7.37 MeV, respectively, have been obtained. Further spin-parity restrictions, lifetime limits, excitation energies, branching ratios and multipole mixing ratios are reported. Discrepancies with previous J^π assignments are discussed in detail.     

The 2425 keV state in 21Na as a subtreshold resonance in 20Ne (p,γ)21 Na

The high-energy tail of the $\text{J}{}^{\mathrm{\pi }}\text{=}\text{1}\text{2}{}^{\mathrm{+}}$, 2425 keV state in ²¹Na, bound by 7 keV against proton decay, has been observed in the ²⁰Ne (p,γ)²¹Na reaction at E_p=0.5?1.5 MeV. The observed excitation function is consistent with a single-level Breit-Wigner shape with Γ_γ=0.31±0.07 eV at E_x = 2425 keV.     

Alpha capture to the giant dipole resonances of 42Ca, 44Ca and 52Cr

Differential cross sections for the ${}^{38}\text{Ar}\text{(α, γ}{}_0\text{)}{}^{42}\text{Ca}\text{,}{}^{40}\text{Ar}\text{(α, γ}{}_{\mathrm{0,\; 1}}\text{)}{}^{44}\text{Ca and}{}^{48}\text{Ti}\text{(α, γ}{}_{\mathrm{0,\; 1}}\text{)}{}^{52}\text{Cr}$ reactions were measured at 90° to the beam direction in 50 or 100 keV steps over the bombarding energy ranges 6.0–15.0 MeV, 5.5–11.1 MeV and 6.0–12.0 MeV respectively. Gamma-ray angular distributions were measured at forty bombarding energies. These show that the (α, γ₀) reaction proceeds through 1^? levels and to a lesser extent 2⁺ levels, whereas the (α, γ₁) reaction most probably proceeds through 1^? and 3^? levels. It is deduced that 〈Γ〉/〈D〉 ≦ 1 for the ⁴⁰Ar(α, γ)⁴⁴Ca. reaction whereas the fine structure observed in the ⁴⁸Ti(α, γ)⁵²Cr reaction is probably due to fluctuations. From a comparison with other data it is shown that the (α, γ) reaction is most probably statistical in nature. Using Hauser-Feshbach theory it is deduced that the ³⁶Ar(α, γ)⁴⁰Ca. reaction is inhibited by isospin selection rules and an estimate is made of isospin mixing in the ⁴⁰Ca giant dipole resonance. The ${}^{38}\text{Ar}\text{(α, γ)}{}^2{}^{42}\text{Ca and}{}^{40}\text{Ar}\text{(α, γ)}{}^{44}\text{Ca}$ data are considered with respect to theories of isosopin splitting of the giant dipole resonance.     

Electromagnetic decay of fragmented analogue states in 45Sc

The ⁴⁴Ca(p, γ) reaction was studied for 45 resonances for E_p = 1.6?2.2 MeV. The overall proton energy resolution was 300–350 eV; the γ-rays were detected with both NaI(T1) and Ge(Li) detectors. Partial and total γ-ray widths were measured for each of the fine structure states of the $\text{3}\text{2}{}^{\mathrm{?}}$ and $\text{1}\text{2}{}^{\mathrm{?}}$ analogue states at E_p = 1.65 and 2.04 MeV, respectively. The data are examined for correlations between the partial widths (Γ_p, Γ_p′, Γ_γi, Γ_γ^total) in different channels. The γ-ray intensities are compared with (τ, d) spectroscopic factors.     

Search for 8+ strength in 16O via the 12C(α, α2)12C1(7.66 MeV) reaction

Closely spaced angular distributions have been measured for the ${}^{12}\text{C}\text{(α, α}{}_2\text{)}{}^{12}\text{C}\text{1(7.66}\text{MeV}\text{)}$ reaction between E_α = 17.39 and 20.5 MeV in a search for 8⁺ strength in ¹⁶O. No evidence of 8⁺ strength is found, but evidence is found for a narrow 7^? resonance at 21.52 MeV excitation.     

Search for highly excited states in 8Be

Excitation functions and angular distributions of the reactions ${}^7\text{Li}\text{(}\text{p}\text{, α)α}{}^1$ and ${}^6\text{(}\text{Li}\text{(}\text{d}\text{, α)α}{}^1$ have b investigated for the excitation-energy region E_X = 21?28 MeV in ⁸Be ($\text{α}{}^1$ denotes the first excited state of the α-particle). pronounced resonant structure has been observed in both channels around E_X = 24 MeV. It is excited simultaneously by odd and even angular momenta. The experimental results are discussed in the light of two models, the αα¹ cluster model and the symplectic model which take into account the configuration interaction (core excitation) in different manners.     

Spin-parity assignments to high-spin states of 41K and 41Ca

Yrast states of ⁴¹K and ⁴¹Ca have been investigated with the ²⁶Mg(¹⁸O, p2nγ)⁴¹K and ²⁶Mg(¹⁸O, 3nγ)⁴¹Ca reactions at a beam energy of 34 MeV. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization measurements were performed with a Ge(Li)-NaI(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{=}\text{7}\text{2}{}^{\mathrm{+}}$, $\text{11}\text{2}{}^{\mathrm{+}}$, $\text{11}\text{2}{}^{\mathrm{?}}$, $\text{13}\text{2}{}^{\mathrm{+}}$, $\text{15}\text{2}{}^{\mathrm{?}}$ and $\text{19}\text{2}{}^{\mathrm{?}}$ to the ⁴¹K levels at E_x = 1.68, 2.53, 2.76, 2.77, 4.27 and 4.98 MeV and of $\text{9}\text{2}{}^{\mathrm{+}}\text{,}\text{11}\text{2}{}^{\mathrm{+}}\text{and}\text{15}\text{2}{}^{\mathrm{+}}$to the ⁴¹Ca levels at E_x = 3.20, 3.37 and 3.83 MeV, respectively, have been obtained. Excitation energies, branching ratios, multipole mixing ratios and transition strengths are reported. The main features of the ⁴¹K and ⁴¹Ca level and decay schemes are reproduced in a 2p-1h and 3p-2h shell-model calculation.     

Lifetimes of low-lying states in 19F

Lifetimes of low-lying states in ¹⁹F were measured using the Doppler-shift attenuation method through the ¹⁵N(α, γ)¹⁹F reaction. Values of τ_m = 3700 ± 700 fs (1.35 MeV), 140 ± 15 (1.46), 19 ± 7 (4.00) and 63 ± 19 (4.03) were obtained for the lowest $\text{5}\text{2}{}^{\mathrm{?}}$, $\text{3}\text{2}{}^{\mathrm{?}}$, $\text{7}\text{2}{}^{\mathrm{?}}$ and $\text{9}\text{2}{}^{\mathrm{?}}$ members, respectively, of the $\text{K}{}^{\mathrm{\pi }}\text{=}\text{1}\text{2}{}^{\mathrm{?}}$ rotational band and 5 ± 3 fs (1.55 MeV) and 370 ± 25 (2.78) for the $\text{3}\text{2}{}^{\mathrm{+}}$ and $\text{9}\text{2}{}^{\mathrm{+}}$ members of the $\text{K}{}^{\mathrm{\pi }}\text{=}\text{1}\text{2}{}^{\mathrm{+}}$ ground-state band. For the Doppler-shift attenuation analysis correction factors of the nuclear and electronic stopping powers were determined by measuring the Doppler-shift attenuation and γ-ray line shape of the 2.78 → 0.20 MeV transition and range values of 100, 200. 300 and 370 keV ¹⁹F nuclei in tantalum. All calculations were done with Monte Carlo methods. The transition strengths are discussed in terms of different theoretical predictions.     

12C(6Li,d)16O and16O(6Li,d)20Ne at E(6Li) = 42 MeV

Spectra up to 25 MeV excitation in ¹⁶O have been obtained from ¹²C(⁶Li, d) at 42 MeV bombarding energy. Angular distributions have been measured for ten states, including two J^π = 1^? states of astrophysical interest, and appear to be mostly direct α-transfer. In addition, data for ¹⁶(⁶Li, d)²⁰Ne(g.s.) and ²⁰Ne¹(2⁺) have been obtained. Excitation energies and widths have been extracted for states in ¹⁶O, including several states at E_x > 15 MeV. Alpha spectroscopic factors, S_α, and reduced α-widths, γ²_α and θ²_α have been deduced for levels in ¹⁶O and ²⁰Ne and compared with theoretical predictions. The J^π = 1^? levels in ¹⁶O at 7.12 and 9.6 MeV excitation appear to have comparable S_α and γ²_α values, viz. $\text{γ}{}^2{}_{\mathrm{\alpha }}\text{(7.12 MeV)}\text{γ}{}^2{}_{\mathrm{\alpha }}\text{(9.6}\text{MeV}\text{) = 0.6}{}^{\mathrm{+1.7}}{}_{\mathrm{?0.3}}$. Both states have apparent S_α and γ²_α values smaller than that for the J^π = 2⁺ “α-cluster” state at 6.9 MeV however. Furthermore, the observed line shape for the J^α = 1^?, 9.6 MeV level indicates Γ_c.m. = 400 ± 50 keV, which is substantially less than the accepted width for this level Γ_c.m. = 510±60 keV). The possible implications of these results for stellar helium burning calculations are discussed.     

High-spin states in 40K investigated with the 26MG + 16O reaction

Yrast levels in ⁴⁰K and ⁴⁰Ar have been investigated with the ²⁶Mg(¹⁶O, pnγ)⁴⁰K and ²⁶Mg(¹⁶O, 2pγ)⁴⁰Ar reactions at a beam energy of 34 MeV. Gamma-ray angular distribution and γ-γ coincidence measurements have been performed with a high-resolution large volume Ge(Li)-NaI(Tl) Compton-suppression spectrometer. Gamma-ray linear polarizations have been measured with a three-crystal Ge(Li) Compton polarimeter. The ⁴⁰K decay scheme involves new high-spin levels at E_tx = 4365.6±0.3, 4875.6±0.4 and 6227.0±0.5 keV with lifetime limits of < 1, < 1 and < 2ps, respectively. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{= 5}{}^{\mathrm{?}}\text{, 6}{}^{\mathrm{+}}\text{, 8}{}^{\mathrm{+}}\text{, 9}{}^{\mathrm{+}}\text{and}\text{(8, 10)}{}^{\mathrm{?}}$ to the ⁴⁰K levels at E_x = 0.89, 2.88, 4.37, 4.88 and 6.23 and of $\text{J}{}^{\mathrm{\pi }}\text{= 4}{}^{\mathrm{+}}\text{and}\text{6}{}^{\mathrm{+}}\text{to the}{}^{40}\text{Ar}$ levels at E_x = 2.89 and 3.46 MeV, respectively, have been obtained. Branching ratios and multipole mixing ratios are reported.     

Band structures in 98Ru and 99Ru

The level schemes of ^{98, 99}Ru were studied with the reactions ⁹⁸Mo(α, 3nγ) and ⁹⁸Mo(α, 4nγ) at E_α = 35 to 55 MeV, using a large variety of in-beam γ-ray detection techniques and conversion-electron measurements. A search for the 3^? state was carried out with the reaction ⁹⁸Ru(p, p′). The ground-state band of ⁹⁸Ru was excited up to J^π = (12)⁺ and a negative-parity band up to (15)^?. New levels in ⁹⁸Ru were found at E_x = 2285 (J^π = 4⁺), 2435 (J^π = (3^?, 4⁺)), 2671, 3540, 4224, 4847, 4915 (J^π = (12)⁺), 4989 (J^π = (12⁺)), 5521 (J^π = (13)^?), 5889, 6591 (J^π = (15)^?), and 7621 keV. New unambiguous spin and parity assignments were made for the levels at E_x = 2014 and 3852 keV, as J^π = 3⁺ and 9^?, respectively. New levels in ⁹⁹Ru were found at E_x = 1976, 2021 ($\text{J}{}^{\mathrm{\pi }}\text{= (}\text{15}\text{2}{}^{\mathrm{+}}\text{)}$), 2393, 2401 ($\text{J}{}^{\mathrm{\pi }}\text{= (}\text{17}\text{2}{}^{\mathrm{+}}\text{)}$), 2875 (π = (+)), 3037, 3201 ($\text{J}{}^{\mathrm{\pi }}\text{= (}\text{23}\text{2}\text{)}{}^{\mathrm{?}}$), 3460 ($\text{J = (}\text{17}\text{2}\text{)}$), 3484 ($\text{J}{}^{\mathrm{\pi }}\text{= (}\text{21}\text{2}{}^{\mathrm{+}}\text{)}$), 3985, 4224 ($\text{J}{}^{\mathrm{\pi }}\text{= (}\text{27}\text{2}{}^{\mathrm{?}}\text{)}$), and 5359 keV. The 1070 keV, $\text{J}{}^{\mathrm{\pi }}\text{=}\text{11}\text{2}{}^{\mathrm{?}}$ level in ⁹⁹Ru has a half-life of 2.8 ns. A strongly excited negative-parity band is built on this level. A positive-parity band based on the ground state was excited up to $\text{J}{}^{\mathrm{\pi }}\text{= (}\text{21}\text{2}{}^{\mathrm{+}}\text{)}$. The level schemes are well reproduced by the interacting boson model in the vibrational limit.     

The second 132+ state in 19F

A cryogenically pumped gas target has been used to study resonances in the ¹⁵N(α, γ)¹⁹F reaction for E_α = 5.1 to 8.6 Mev. Gamma-ray intensity and angular distribution measurements for a resonance at E_α = 8.105 Mev, corresponding to a state at 10.411 MeV in ¹⁹F, restrict the spin and parity of the state to $\text{11}\text{2}{}^{\mathrm{+}}$ or $\text{13}\text{2}{}^{\mathrm{+}}$. Comparison with shell model calculations indicate that the state is a strong candidate for the second $\text{13}\text{2}{}^{\mathrm{+}}$ (2s, 1d)³ level in ¹⁹F.     

Proton spectra from the 6,7Li(γ,p) 5,6He reactions at Eγ = 60 MeV

The ${}^{\mathrm{6,7}}\text{Li}\text{(γ,}\text{p}\text{)}$ reactions have been investigated for E_γ = 60 MeV. Excitation of residual (1p)^?1 and (1s)^?1 hole states is evident from the proton spectra measured at ?_p = 45°. The data are compared with a theoretical calculation which includes short-range correlations.     

Observation of particle unstable 4H in pion absorption in 7Li

A particle unstable state of ⁴H has been identified in the reaction $\text{π}{}^{\mathrm{?}}\text{+}{}^7\text{Li}\text{→}{}^4\text{H+t}\text{,}{}^4\text{H}\text{→}\text{t}\text{+π}$ by observing the two emitted tritons. A resonance energy E_Γ=(2.7±0.6) MeV and a reduced width γ²=(2.3±0.6) MeV were deduced, in agreement with the parameters of the ground-state level (J^π=2^?) found in the p-wave of n-t-scattering. The yield per stopped pion is (5.6±1.8)×10^?4. Previous measurements in pion absorption are in disagreement with our results.     

Generalized neutron particle-hole states in an extended unified model

Negative-parity levels in the doubly even N = 82, Z nuclei, with 3.0 MeV ? E_x? 6.0 MeV are described in an extended unified-model approach, where neutron hole states in the Z = 50, N = 82 closed shell core, (i.e. ) are coupled to the low-lying levels (E_x ? 2.0 MeV) of the odd-neutron N = 83, Z nuclei. This particular configuration space of generalized neutron particle-hole states (GNPH) is particularly suited for describing negative-parity levels obtained in proton inelastic scattering through isobaric analogue resonances (IAR), corresponding to the N = 83, Z low-lying nuclear levels. Level schemes as well as partial decay widths and angular distributions are calculated and compared extensively with the available experimental data. Also spectroscopic factors, as well as wave functions, deduced from the experimental results are studied in detail. Thus in the cases of ¹³⁶Xe, ¹³⁸Ba, ¹⁴⁰Ce, ¹⁴²Nd and ¹⁴⁴Sm, some of the important neutron particle-hole configurations can uniquely be determined in the energy region 3.0 MeV ?E_x ? 6.0 MeV.     

High-spin negative parity states in 19F

Levels at 7.17, 8.29, 8.96 and 9.88 MeV in ¹⁹F have been assigned spin and parity $\text{11}\text{2}{}^{\mathrm{?}}$, $\text{13}\text{2}{}^{\mathrm{?}}$, $\text{11}\text{2}{}^{\mathrm{?}}$ and $\text{11}\text{2}{}^{\mathrm{?}}$, respectively, from resonance strength and γ-ray angular distribution measurements employing the ¹⁵N(α,γ) ¹⁹F reaction. An earlier assignment of $\text{11}\text{2}{}^{\mathrm{+}}$ to the 8.96 MeV level is incorrect. The measured properties of the $\text{11}\text{2}{}^{\mathrm{?}}$ states are compared with the results of both SU (3) shell model and cluster model calculations.